Method for transmitting data via a serial communication bus, correspondingly designed bus interface, and correspondingly designed computer program

ABSTRACT

A method for transmitting data via a serial communication bus where the data are transmitted with an adapted transmission frame. The adapted transmission frame includes at least one arbitration field and a data field, with the arbitration field being used to control the bus access in accordance with the Carrier Sense Multiple Access with Collision Resolution method by prioritization of messages with the aid of an identifier. For the arbitration phase, a low bit rate is set; and an increased bit rate is set for the transmission of the data in the data field. A start field is provided in the transmission frame. The data are packaged as an Ethernet transmission frame, which is inserted into the data field of the adapted transmission frame. The arbitration field and the start field replace a preamble and a Start Frame Delimiter of the Ethernet transmission frame.

PRIORITY CLAIM

This patent application is a U.S. National Phase of International PatentApplication No. PCT/EP2018/071361, filed 7 Aug. 2018, which claimspriority to German Patent Application No. 10 2017 213 812.2, filed 8Aug. 2017, the disclosures of which are incorporated herein by referencein their entireties.

SUMMARY

Illustrative embodiments relate to the technical field of serial datatransmission between electronic components, in particular, controlunits, sensors and actuators, which are interconnected via a bus system.Such control units are widely used in transportation vehicles. Networkedcontrol units, sensors and actuators are also used in other fields oftechnology, e.g., in automation technology, process engineering, etc.Illustrative embodiments also relate to a suitably designed businterface and to a suitably designed computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are shown in the drawings and are explained inmore detail in the following by reference to the figures. Shown are:

FIG. 1 shows a transportation vehicle with the transportation vehicleelectronics components for the areas of powertrain, suspension anddriver assistance;

FIG. 2 shows a block diagram for a transportation vehicle on-boardnetwork for the areas of drivetrain, suspension and driver assistance;

FIG. 3 shows a block diagram for the transportation vehicle on-boardnetwork for the area of driver assistance;

FIG. 4 shows the detailed transmission frame format of an Ethernet frameaccording to the IEEE 802.1Q specification;

FIG. 5 shows the detailed transmission frame format according to a firstexemplary embodiment for transmitting a basic Ethernet frame;

FIG. 6 shows the individual bits in the CRC field in accordance with thenew transmission frame format;

FIG. 7 shows the detailed transmission frame format according to asecond exemplary embodiment for transmitting a “tagged” Ethernet frame;and

FIG. 8 shows an example of the processing of the arbitration phase forthe new transmission frame format when two network nodes access the busat the same time.

DETAILED DESCRIPTION

In modern transportation vehicles, a plurality of control units areinstalled. A number of control units are used for the powertrain alone,such as the engine control unit, transmission control unit, ESP controlunit and others. It is also worth mentioning the category of controlunits, which are responsible for regulation processes in the area ofsuspension systems. These are control units for electronic suspensionadjustment or control units for driving dynamics control or controlunits which provide steering assistance, such as speed-sensitive powersteering. In addition, there are other control units that are installedin the area of the transportation vehicle bodywork and provide certaincomfort functions. Examples of these include the electric door or windowcontrol units, air-conditioning control units, seat adjustment controlunits, airbag control units and similar devices. Then there is also theclass of control units associated with the infotainment area, such as acamera control unit for environment monitoring, navigation device, radaror lidar equipment, communication module and entertainment module withTV, radio, video and music function.

There is a trend in the technology towards increasing use of IPcommunications, such as IPv6 or IPv4, for the transportationvehicle-internal networking of control units. This method works bytransmission of IP packets, which can have a length of up to 64 Kbytes.Although the IP packets can be transmitted in segmented form, the use ofIP communication still requires a bus technology to be used that cantransmit sufficiently large messages.

Typically, the control units of the different categories are eachnetworked with a separate bus appropriately designed for the category ofdevice. Several different bus systems can therefore be used in thetransportation vehicle. The different bus systems can be interconnectedvia gateways to allow a data exchange. In the area of powertrain controlunits, the CAN bus is typically used, as is also the case in the area ofcomfort control units. In the infotainment area, other bus systems arealso commonly used, such as bus systems based on Ethernet technology,e.g., AVB (Audio Video Bridging), which is based on the standard familyaccording to the IEEE 802.3 standard. Bus systems in which the datatransmission takes place via fiber-optic cables can also be used.Examples to be cited are the MOST bus (Media Oriented System Transport)or the D2B bus (Domestic Digital Bus).

The Ethernet bus system dates back to the early days of networkingcomputers and was developed at the Palo Alto Research Center, Xerox PARCin the late 1970s. From as early as 1980 the Institute of Electrical andElectronics Engineers (IEEE) has been responsible for the maintenanceand further development of Ethernet. The 802 working group isresponsible for Ethernet. The Ethernet-related standards are thereforeidentified with a prefix 802 (e.g., IEEE 802.1, IEEE 802.2, IEEE 802.3,etc.).

One of the great strengths of Ethernet is that ready-to-use protocolsexist for the transport of a variety of user data, such as video/audiodata, etc., and that today a wide range of physical media are supportedwhich allow them to be used in transportation vehicles. Since thephysical media are independent of the transmission protocol, othertransmission techniques can also easily be developed and adapted to therequirements of the automotive industry.

It is required if the IPv6 protocol is to be used, that packets of atleast 1280 bytes in size can be transmitted as the MTU (MaximumTransmission Unit), as it is known in the Ethernet standard. However,neither the classical CAN Bus 2.0, standing for Controller Area Network,used in transportation vehicles nor the already extended CAN FD Bus,standing for Controller Area Network Flexible Data Rate, satisfies thisrequirement since they can only transmit messages with a maximum size of8 and 64 bytes respectively. This makes the use of the CAN busunsuitable if it is to support the required IPv6 communication. Furtherdetails of the IPv6 protocol can be found in the RFC 2460 Specificationfrom the Internet Engineering Task Force IETF.

Up to now, in the automotive sector IPv6 communication has hardly beenused, since it involves high resource consumption. The standard approachto enable IPv6 communication is to use Ethernet technology, which isexpensive for the automotive industry, as a networking technology.

For the automotive industry, the options IEEE 100BASE-T1 and IEEE1000BASE-T1 have been developed. In this case, the transmission of datain the forward and reverse direction can be implemented using only asingle twisted pair of wires. There is a Physical Layer Block, which isinstalled in a control unit (ECU) as a separate module/chip. This blockprovides the connection between the physical medium (network cable) andthe Ethernet Controller Block.

In this Ethernet option, only two nodes are ever connected to one busline. The only topology available is therefore the point-to-pointconnection. More than two nodes can be connected by a coupling element.This usually involves the use of a network switch, which as a Layer-2coupling element allows the connection to multiple physical connectionsand can forward messages from branch to branch independently. This isone of the biggest drawbacks of the Ethernet bus system in theautomotive field, because it increases costs.

In the automotive sector therefore, the use of the CAN bus (ControllerArea Network) in accordance with an ISO standard tends to dominate. TheCAN bus was developed in the 1980s and standardized in 1994. Thecorresponding ISO standard has the number ISO 11898. There is a standardfor the high-speed range up to 1 Mbit/s, which is the ISO 11898-2standard. Then there is a standard for the low-speed range up to 125Kbit/s, which is the ISO 11898-3 standard. The ever-growing volumes ofdata result in ever higher bus loads on the CAN buses. This led to afurther development of the CAN bus. The extended CAN bus is known underthe term CAN FD bus. FD stands for flexible data rate. In this option ofthe CAN bus different data rates are selected. For the arbitrationphase, the data rate remains low, as in the classical CAN bus. For thetransmission of user data the transmission is switched to a higher datarate. If the user data in a CAN-FD message is transmitted faster, thenthe period for which the bus is occupied is reduced; and the load on thebus is reduced. If the transmission duration remains in the same timeframe as in classical CAN messages, larger amounts of data could betransported with a CAN-FD message. This method was also implemented inCAN FD. Instead of the 8-byte long user data field, in CAN FD a 64-byteuser data field is used. In one implementation the data rate for thetransmission of the user data field increases, for example, from 500Kbit/s to 2 Mbit/s.

Disclosed embodiments overcome the described drawbacks in theintroduction of IP communications in the automotive sector. Disclosedembodiments enable large Ethernet frames, so-called “jumbo frames”, tobe transmitted over the transportation vehicle bus without segmentation.The proven linear bus topology in the transportation vehicle is designedto be supported, where several control units are networked without theuse of a switch as a coupling element. This bus structure is optimalwith regard to the cabling required and overall cost. On the part of theIEEE organization, an improved 10 Mbit/s Ethernet option will berequired to cope with these points. The bus subscribers will beavailable to split up the 10 Mbit/s of available bandwidth. The newtransmission protocol should also be capable of real-time operation. Atthe same time, it should be able to be administered locally. This meansthat it may not be necessary to supply all subscribers of the networkwith an identical configuration. This makes it possible to significantlyreduce development costs. A prioritization of the subscribers as well asthe data to be transferred must be allowed. A further requirement isthat the Ethernet frame format according to IEEE 802.1Q should besupported.

Disclosed embodiments provide a method for transmitting data over aserial communication bus, a correspondingly designed bus interface, anda correspondingly designed computer program.

To achieve this, a method for transmitting data over a serialcommunication bus is followed, in which the data are transmitted with amodified transmission frame. The modified transmission frame has atleast one arbitration field and one data field, wherein the arbitrationfield is used to control the bus access according to the CSMA-CR method,which stands for Carrier Sense Multiple Access with CollisionResolution, by prioritization of the messages based on an identifier. Alow bit rate is set for the arbitration phase and an increased bit rateis set for the transmission of the data in the data field. A start fieldis provided in the transmission frame and the data are packaged as anEthernet transmission frame, which in turn is inserted into the datafield of the modified transmission frame. The arbitration field and thestart field thus replace a preamble and a start frame delimiter of theEthernet transmission frame. The Ethernet transmission frame could be anEthernet transmission frame according to the option IEEE 802.1Q.

The great advantage here is that a content-dependent, fine-grainedpriority-based arbitration is combined with Ethernet to produce anetworking technology which is very well suited to the needs ofautomotive networking. The system can also be administered in adecentralized manner, as is the case today with the CAN bus. This allowsa high degree of flexibility in the development process, in thatindividual control units in the network can be modified and furtherdeveloped independently of the others. For the bus topology it is alsopossible to use the linear bus structure, i.e., many stations cancommunicate with each other at very low system costs.

The increased data rate can be fully utilized, i.e., data rates up to 10Mbit/s and above can be achieved. Also, it is possible to choose thedata rate relatively freely depending on the network size and thecommunication scenario.

In addition, the existing mechanisms from the CAN FD bus for evaluatingthe real-time capability, for example, can be adopted. At the same time,due to the maintenance of the Ethernet frame format, device addressingbased on the well-known Ethernet MAC addresses can be implemented.Furthermore, on account of the large MTU (Maximum Transmission Unit)which it inherits from the Ethernet standard, the network is ideallysuited to transportation vehicle-internal IP communication.

Also, from the point of view of interoperability with other Ethernetnetworks which will be present in the transportation vehicle in thefuture, this solution is beneficial. This means that the Ethernet framecan be easily extracted from the modified transmission frame and thenfed to a router or network switch for forwarding to other subnets.

A particularly beneficial measure relates to the assignment of theidentifiers in the arbitration field for the prioritization of themessages. According to this, the identifier in the arbitration field isdivided into the areas of “Message Content” identifier and “Device”identifier. By the appropriate assignment of the device ID, one bus nodecan be given priority over the other subscribers on the bus. As aresult, the network behavior can be planned/predicted and is thereforereal-time capable. One constraint is that a unique device identifier isassigned to each device. This measure is particularly useful whenmultiple similar control units, actuators or sensors are networked viathe communication bus.

In a simplified option, all bits of the identifier, for example, 32bits, are used for the message content identification andprioritization. The device addressing is performed solely by the MACaddresses which are also transmitted in the modified transmission frame.

It is beneficial here if the section with the higher order bits isreserved for the prioritization of the message content and the sectionwith the lower order bits is allocated to the device identification. Asa result, as in the CAN bus, during the arbitration phase the bus accessmakes decisions primarily based on the message contents with differentassigned priorities and only uses the device ID as a secondarycriterion.

In an alternative design a 32-bit long identifier is sub-divided suchthat 24 bits are reserved for the prioritization of the message contentand 8 bits are provided for the prioritization of the device.

In some disclosed embodiments, the data field has a variable length upto a specified upper limit. The variability of the length of the datafield guarantees many application possibilities. This means that nocompromise need be made if the particular application requires a highnet data rate, or in another case if the real-time capability is more ofa priority and low latency times are more important.

Here it is particularly beneficial if a range of 0 to 4096 bytes isspecified for the variable length of the data field. This allows a goodinteroperability with the now widely applicable 1 Gbit Ethernet option.Routing between a part of the transportation vehicle network where the 1Gbit Ethernet bus option is used would then be possible withoutsegmentation. The use of IP communication then becomes possible in astraightforward way.

It is also beneficial if the length of the arbitration field is set to32 bits. This measure simplifies the hardware development for themodified bus. Register lengths commonly used today are typically amultiple of one byte, i.e., a multiple of 8 bits.

It is also beneficial if a control field is provided between thearbitration field and data field in the modified transmission frame, inwhich at least one section is allocated for the length specification interms of the data field. Here, this section therefore needs to belengthened to be able to specify the full length of 4096 bytes. Thisrequires 13 bits.

A CRC field can also be specified in the transmission frame, in which atleast one section is provided for a CRC check code. The CRC check codeis used for error detection in accordance with the well-known cyclicredundancy check algorithm. Here, it is beneficial if a start field isprovided in the transmission frame and the CRC code is calculated overthe start field, control field, arbitration field and data field.

In this case it is particularly beneficial if the CRC check codeprovided in the Ethernet transmission frame is replaced by an extendedCRC check code and this is inserted into an extended CRC field (CRC) ofthe modified transmission frame. The extended CRC check code iscalculated over the start field (SOF), arbitration field (BA), controlfield (DL), destination address field (DA), the source address field(SA), optional Q-TAG field (QTAG), type field (ET), data field (PL) andthe section of the stuff-bit counter in the CRC field (CRC).

The same applies to the use of a bit-stuffing method, for example, onewhich was already used in the CAN 2.0 protocol and the CAN FD protocol.A beneficial feature here is that the data transmission takes placeasynchronously and to ensure the synchronization of the datatransmitting station and data receiving station a resynchronization isperformed according to a bit-stuffing rule, the bit-stuffing rule beingapplied over the fields from the start field up to the end of the datafield, and the number of the inserted stuff-bits being entered in asection of the CRC field as a check. The insertion of a stuff-bit forcesan edge change on the bus, which is used in the CAN controller forresynchronization of the timer, which sets the sampling rate for the bitrecovery when receiving data. A modified bit-stuffing rule is used inthis case. The bit-stuffing algorithm (frame encoding) for the newtransmission format is modified to the effect that a stuff-bit isinserted only after 10 consecutive bits with the same bus level, and notafter 5 bits as in CAN 2.0 and CAN FD. This means fewer overhead bitsare needed in the data frame, which increases the efficiency of the datatransmission.

It is beneficial if an end field is also provided in the transmissionframe and at least one end-of-frame code is entered in the end field,wherein the end-of-frame code has a length of 11 bits. This measure isbeneficial due to the modified bit-stuffing rule. Sending theend-of-frame code enforces a violation of the new bit-stuffing rule, sothat subscribers that were not synchronized properly detect this factand can reset the CAN controller so that they can become correctlysynchronized again.

In the CRC field the bit-stuffing rule in accordance with the extendedprotocol is not used. Therefore it is also beneficial if a stuff-bit isforcibly inserted in the CRC field at fixed specified positions. Edgechanges are thus also guaranteed in the CRC field and the CANcontrollers of the bus subscribers remain synchronized.

In an example, the CRC field begins with a fixed specified stuff-bit andthe other fixed stuff-bits are each inserted at an interval of 9 bits ofthe CRC field. The fixed specified stuff-bit is complementary to itspredecessor bit.

For an appropriately designed bus interface for use in the proposedmethod for the transmission of data over a serial communication bus, thesame benefits as those described in relation to the corresponding methodoperations apply.

The same applies to an appropriately designed computer program, whichwhen processed in a computation unit executes the transmitter-sideoperations and/or the receiver-side operations of the proposed methodfor transmitting data. Hardware costs are of course a key factor in theautomotive sector, where less powerful microcontrollers are thereforemainly used which are supported by separate CAN controllers, in whichthe data transfer protocol is implemented by special hardware. In otherareas, for example, in the fieldbus sector for automation technology orprocess engineering, more powerful microcontrollers are also used, forwhich the software solution then also becomes an option for implementingthe extended data transmission protocol.

The following description illustrates the principles of the disclosure.It goes without saying, therefore, that persons skilled in the art willbe in a position to design different arrangements which, although notexplicitly described here, nevertheless embody the principles of thedisclosure and are also intended to fall within its scope of protection.

FIG. 1 shows a transportation vehicle 10 with various electroniccomponents. The transportation vehicle shown here is a passenger car.Any other type of vehicle could also be considered as the vehicle,however. Examples of other vehicles are: buses, commercial vehicles, inparticular, lorries, agricultural machinery, construction vehicles,motorcycles, rail vehicles, etc. The use of the disclosed embodimentswould also be possible in general in agricultural vehicles, railvehicles, water-borne vehicles and aircraft. The use of the disclosedembodiments is intended primarily for the automotive sector. However, asin the case of the CAN bus it could conceivably also be used in thefieldbus sector, i.e., in automation technology, process engineering,etc. A plurality of electronic control units are used in a moderntransportation vehicle. FIG. 1 shows the networking of some of thecontrol units and sensors. Three different classes of control units canbe distinguished. The control units of each class are networkedseparately. The respective communication buses are connected via acentral gateway controller 140. The control units of the class ofcontrol units for the driver assistance area are networked via the bus102. The control units connected to this are the driver assistancecontrol unit 111, RADAR unit 112 and ultrasonic sensor control unit 113.The purpose of the RADAR device (standing for Radio Detection andRanging) is to implement a cruise control/speed limiter or to implementa distance warning or collision warning device. It is also possible touse a LIDAR (Light Detection And Ranging) device in addition or as analternative.

The control units of the class of control units for the powertrain arenetworked via the bus 104. The control units connected to this are theengine control unit 121, ESP control unit 122 and transmission controlunit 123. Also connected to the bus 104 are the wheel speed sensors 124to 127. The control units of the class of control units for thesuspension area are networked via the bus 106. The control unitsconnected to this are the suspension control unit 131 and thepower-assisted steering control unit 132.

FIG. 2 shows the corresponding block diagram for the automotiveelectronics in the areas of powertrain, suspension and driver assistancesystem. Identical reference numerals in FIG. 2 designate the samecomponents as in FIG. 1. The three separate communication buses 102,104, 106 are implemented as linear buses. That being the case, the busprotocols can be designed for the communication buses 102, 104 and 106according to the needs of the control units that are networked there.For example, it might be useful to design the communication bus 106 forthe suspension area with a higher data rate than the two communicationbuses 102 and 104. Sensor signals that are relevant to the suspension,e.g., the comfort feature of pothole detection, must be responded toextremely quickly to adjust the damper setting accordingly.

To allow the exchange of data between subscribers connected to differentcommunication buses 102, 104, 106, the gateway 140 is provided. This isconnected to all three different bus systems 102, 104 and 106. Thegateway 140 is designed to convert the data packets that it receives viathe one communication bus so that they can be forwarded there in thetransmission format of the other communication bus. As shown, as acentral device the gateway 140 is connected both to the bus 102, the bus104 and to the bus 106. It therefore performs all the necessary formatconversions when data need to be exchanged between the various bussystems.

As mentioned at the beginning, a communication bus is to be used whichalso allows larger data packets according to the IPv4 or IPv6 protocolto be transmitted. To achieve this the use of an option of the Ethernetstandard family makes sense. Here, ready-to-use transmission protocolsare already available, such as IP (Internet Protocol), UDP (UserDatagram Protocol), RTP (Real-Time Transport Protocol), TCP(Transmission Control Protocol). The development effort in terms of thetransmission protocols is thus kept within limits. The Ethernet networktechnology corresponds fully to the IEEE standard 802.3. Specialvariations of this technology have been developed for use intransportation vehicles. Two of these options are the above-mentioned100BASE-T1 option and the 1000BASE-T1 option of the Ethernet standardfamily. The automotive industry has specified the physical layer as acommunication standard for automotive Ethernet. This standard ispublished by the IEEE in two variations as 100BASE-T1 and 1000BASE-T1 aspart of the specification IEEE P802.3bp.

A twisted-pair cable is used as the physical transmission medium in bothoptions, to which symmetrical differential voltages are applied for thetransmission of information. The voltages represent symbols that atransmitter generates (in encoded form) according to the desiredbitstream. A receiver then uses the symbol stream generated to recoverthe bits contained in it (decoding).

A particularly attractive feature of this physical layer is thatinformation can be transmitted on a UTP cable (a cable with a twistedpair of conductors without shielding, known as unshielded twisted pair)at 100 Mbit/s or 1000 Mbit/s. With only two subscribers even full-duplexmode is possible, i.e., two interconnected nodes can send and receive atthe same time. This is the case for the Ethernet options 100BASE-T1 and1000BASE-T1, because due to the use of the network switch onlypoint-to-point connections are possible there. As a transmitter a nodeadds its own differential voltage on the two conductors, while as areceiver it subtracts its own voltage from the total voltage applied.The result of the subtraction is equal to the voltage that was sent fromthe counterpart. So that differential voltages can be added orsubtracted, the two nodes need to know when a new symbol starts. Thismeans that both nodes must be synchronized to the symbol stream. This iscarried out in IEEE 100BASE-T1 by a master and a slave node. The mastergenerates a continuous symbol stream to which the slave synchronizes.The configuration of the PHY as master or slave is carried out by thecore software of the microcontroller. If there are more subscribers, itis mandatory for a network switch to be provided.

For the reasons already described above, the communication bus 106 forthe suspension area is designed according to the IEEE 1000BASE-T1 optionand the other two buses 102 and 104 according to the IEEE 100BASE-T1option.

The same network cable which is used for the IEEE 100BASE-T1 option ofEthernet can also be used in the CAN bus as the physical transmissionmedium. But in this case full-duplex operation is no longer possible,because several subscribers are connected to the bus. By using thespecial bus arbitration procedure in accordance with CSMA/CR (standingfor Carrier Sense Multiple Access/Collision Resolution, also known asCSMA/CA, standing for Carrier Sense Multiple Access/CollisionAvoidance), data collisions are avoided and exactly one subscriber takescontrol of the bus, so that a network switch can be dispensed with.

The principle of the networking of electronic components using thecommunication bus is shown in more detail in FIG. 3. As an example, thecommunication bus 102 for the area of driver assistance is shown. Allcontrol units 111 to 113 are connected to the communication bus 102.Likewise, the gateway 140 is also connected to the communication bus 102(not shown further). The bus structure of the communication bus 102 islinear. As a bus cable the unshielded twisted pair UTP two-wire cablealready mentioned is used. In each control unit 111 to 113 a busmatching circuit 21 is used for connecting to the bus cable. Acustomized physical layer chip 22 is connected to this. The PHY chip 22essentially corresponds to a CAN transceiver chip, but it is adapted sothat the modified transmission protocol is supported. The referencenumeral 23 denotes the associated modified CAN controller. The referencenumber 24 denotes a microprocessor, on which as the host IC theapplication software is installed. Other network protocols starting fromthe Data Link Layer are installed on this microprocessor 24. TheEthernet MAC frame is supplied by the Ethernet MAC-layer. The associatednetwork protocol stack is installed on the microprocessor 24. The CANcontroller 23 takes the finished Ethernet MAC frame, removes the CRCsection, assembles the modified transmission frame, calculates the CRCcheck code according to the new method and inserts it into the CRCfield. The details will be explained in more detail below. The CRCsection of the Ethernet MAC frame is therefore not included in the UserData field PL, because each time an Ethernet MAC frame is forwarded by anetwork switch the CRC check code is re-calculated anyway. This iscarried out on the MAC layer before transferring data onto the buscable.

FIG. 4 shows the new transmission frame format according to the Ethernetbus option IEEE 100BASE-T1. The so-called tagged MAC frame isillustrated, which may be used in the automotive sector. The lower partof the figure shows the format of an Ethernet packet in this option. Thefirst two sections, preamble and SFD, are only part of the Ethernetpacket. The Ethernet frame proper, also known as the Ethernet MAC frame,only starts after that. To transfer the Ethernet frame an Ethernet PHYadds the preamble and the Start Frame Delimiter (SFD) at the beginning.In IEEE 100BASE-T1 these are used for signaling the start of thetransfer, i.e., for the above-mentioned synchronization. The EthernetMAC frame consists of the fields MAC header, MAC payload and CRC field.The MAC header consists of the sections for destination address, sourceaddress, VLAN tag, EtherType. In the destination address and sourceaddress sections the MAC addresses are entered for the destination andsource respectively. A distinction between basic and tagged MAC frame ismade with the type field EtherType. This generally identifies thepackage contained in the payload field and thereby provides informationabout the protocols used in the higher layers (e.g., IPv4, IPv6). In thetagged MAC frame a VLAN identifier (e.g., 0x8100) is located at thebeginning of the VLAN tag field. If this is present, the type fieldEtherType is moved back by four bytes and the VLAN tag is inserted atits original position.

A VLAN tag consists of a Protocol Identifier (TPID) (corresponding tothe VLAN identifier) and a Control Information (TCI). The TCI consistsof a priority (PCP), a Drop Eligible or Canonical Form Indicator (DEI orCFI) and an identifier (VID). In the automotive industry, Identifier VIDand Priority PCP are mainly used. The Identifier VID identifies therespective virtual network for the different areas of application. Thepriority allows the optimization of propagation times through networkswitches, so that important information can be forwarded expeditiously.

In the user data area of the Ethernet frame (MAC payload) informationwith variable length can be transferred. In the tagged MAC frame thepayload field has a minimum length of 42 bytes. In accordance with theIEEE 100BASE-T1 specification this field can contain up to 1500 bytes.

A CRC checksum is transferred into the CRC field at the end of the MACframe. The value it contains is calculated using a standardizedalgorithm which is implemented identically in the transmitter and thereceiver. The calculation is performed with all fields of the EthernetMAC frame and therefore secures the entire message.

The middle part of FIG. 4 shows the format of an IPv6 packet with a sizeof 1500 bytes. It fits completely in the user data field of the EthernetMAC frame.

Above it a UDP packet is shown, corresponding to User Datagram Protocol.It has a length of 1460 bytes and fits completely in the User Data fieldof the IPv6 packet.

The transmission of a complete Ethernet MAC frame does not now takeplace in accordance with the known Ethernet option IEEE 100BASE-T1.Instead, the distributed multiple bus access method according to CSMA/CRis used. For this purpose, the fields preamble and SFD shown in FIG. 4at the beginning of an Ethernet packet are replaced. They are replacedby the fields SOF (Start of Frame) and BA (Bus Arbitration) known fromthe CAN bus. In contrast to the CAN-FD bus, however, the BA field isextended from 29 bits to 32 bits. This expands the address space for theidentifier within the BA field and fully exploits the typical registervariables found in microcomputers. The control bits SRR, RTR, RRS andIDE known from the CAN-FD bus, which are otherwise provided for thepurpose of controlling the transmission frame format, are omitted.

The various fields of the new transmission frame formats are shown inFIGS. 5 and 6. The names of the various fields are listed in thefollowing table. In subsequent mentions of these fields the full namewill not be repeated.

Field Full Name SOF Start of Frame BA Bus Arbitration DL Data Length DADestination Address SA Source Address ET Ether Type QTAG Q-Tag PLPayload CRC Error Check Sum EOF End of frame

FIG. 5 shows the transmission frame format for the transfer of a basicEthernet frame according to IEEE 802.1Q. In this case, the PL field hasa length of 46-4096 bytes. The length of this field has thus beendramatically increased compared to the length specified in IEEE100BASE-T1. Due to requirements for interoperability with other Ethernetnetworks, the user data field PL must be padded to a minimum length.This is carried out using the well-known “padding” technique. The rulefor the padding technique is: DA+SA+ET+QTAG+PL+CRC>=64 bytes. Takentogether, the fields listed below must result in a minimum length of 64bytes. The value of the length field must correspond to the actuallength of the payload without taking account of the padding bits.

In the Control Field DL the section for the length specification of thedata field is extended to a length of 13 bits. There is no need for theESI bit of the CAN-FD bus at the beginning of the DL field. In the bitsDL0 to DL12 the length of the user data field is specified as the numberof bytes. As a result, the numerical value in this section indicatesexactly the number of bytes in the User Data field. With 13 bits themaximum number of bytes that can be encoded is 8192. But also, any wholenumber in this range can be encoded with it. The length of the datafield should contain up to 4096 bytes, to allow space for anotherEthernet jumbo frame of up to this size. The DL field with 13 bits canspecify more bytes, but it is fixed at 4096 bytes by specification.Therefore, an arbitrary number of bytes within the specified upper limitof 4096 can be entered in the extended data field PL.

The data field PL itself can have a variable length. Depending on thesetting this can be followed by up to a maximum of 4096 bytes. Thiscorresponds to a length of 32768 bits.

The control bits FDF, BRS and the reserved res bit between Control FieldDL and Data Field PL are omitted.

The CRC check code field CRC is extended to a length of 51 bits. This isdue to the simultaneous extension of the data field. In this case thelength of the CRC check code has a value of 32 bits, as before. Butspecial bits are provided for bit-stuffing. The name and position of theindividual bits in the CRC field is shown in FIG. 6.

The CRC field CF in which the CRC check code is entered is extended to aCRC length of 32 bits. The check code is entered in the bit-fields CRC0to CRC31.

To calculate the CRC check code, e.g., the polynomialG(x)=x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1 is used.

The selected polynomial corresponds to the polynomial which is proposedin the IEEE 802.3 specification for Ethernet.

The CRC checksum is calculated from the SOF bit up to the final bit ofthe stuff-bit counter (Stuff0).

The Stuff Count section in the CRC field is modified compared to CAN FDto a length of 12 bits and relates to the bits Stuff0 to Stuff11. Thedata entered in the Stuff Count section is the number of stuff-bitsinserted in the field from the SOF bit up to the final bit of the DataField DF. The number of stuff-bits is binary-coded. The use ofbit-stuffing is simplified however, compared to the bit-stuffing used inthe CAN-FD standard, as described in detail in the following.

The insertion of stuff-bits is used for the purpose of synchronizationin asynchronous data transmission. The synchronous operation of thecommunication partners is established using the signal edge of the startbit SOF of a CAN message changing from recessive to dominant. Aresynchronization mechanism in addition to the SOF bit ensures themaintenance of the synchronous operation. The resynchronizationmechanism is based on the analysis of signal edges changing fromrecessive to dominant. For the synchronization to be maintained here,the bit-stuffing mechanism was introduced into the CAN standard. In theISO standard ISO 11898-1 it is specified that after a maximum of fivehomogeneous bits a complementary bit must be transmitted, even if acomplementary bit would follow after five homogeneous bits anyway. Thelocation of the stuff-bits is known to the receiver due to the rule, andit can ignore the stuff bits.

The bit-stuffing algorithm (frame encoding) for the new transmissionformat is modified to the effect that a stuff-bit is inserted only after10 consecutive bits with the same bus level, rather than after 5 bits.This means fewer overhead bits are needed in the data frame, whichincreases the efficiency of the data transmission.

The variable bit-stuffing is only carried out for the bits from the SOFup to the final bit of the data field PL. From the CRC field on,predefined stuff-bits (FixedStuffx) are used. The FixedStuff bits arealways inserted after 9 bits.

These are the bits FixedStuff0, FixedStuff1, FixedStuff2, FixedStuff3,FixedStuff4 and FixedStuff5. The individual stuff-bits in the CRC fieldare each transmitted with the complementary level of the bit transmittedimmediately preceding it.

As a result of these permanently specified stuff-bits FixedStuff0,FixedStuff1, FixedStuff2, FixedStuff3, FixedStuff4 and FixedStuff5, aguaranteed edge change is effected at the desired location duringtransmission.

The bit FixedStuff0 is transmitted between the last data bit and the bitStuff11.

The bit FixedStuff1 is transmitted between the bit Stuff3 and bitStuff2.

The bit FixedStuff2 is transmitted between the bit CRC26 and bit CRC25.

The bit FixedStuff3 is transmitted between the bit CRC17 and bit CRC16.

The bit FixedStuff4 is transmitted between the bit CRC8 and bit CRC7.

The bit FixedStuff5 is transmitted between the bit CRC0 and bit CRCDe1.

The CRCDe1 bit, which acts as a CRC delimiter, remains unchanged and hasthe same function as in the CAN FD standard.

In the End Field EOF the bits ACK and ACKDel known from the CAN-FD busare omitted.

In the End Field EF, the section with the EOF identifier is extended to11 bits. Here, instead of the standard 7 consecutive recessive bits inthe CAN bus, 11 recessive bits are therefore transmitted. The extensionof the EOF symbol is a consequence of the modification of the stuffingalgorithm. Only after 11 consecutive bits of the same bus level is thenew stuffing rule violated. This is exploited here.

In the CAN bus and CAN-FD bus a so-called Intermission Field is insertedbetween two transmitted data frames. Here, 3 consecutive recessive bitsIFS2 to IFS0 are again transmitted. From these the CAN controllersdetect that the bus has been enabled again. This field can be omitted inthe new transmission format proposed here.

FIG. 7 also shows the transmission frame format for the transmission ofa tagged Ethernet frame according to IEEE 802.1Q. This transmissionframe format differs from the format shown in FIG. 5 only in the factthat the known QTAG field with 4 bytes is also provided between the SAfield and the ET field. As a result of this, the data field PL isshortened to a minimum size of 42 bytes. In principle, the QTAG field isoptional, but it is nevertheless highly likely always to be used. Thedetails of the QTAG field are described in the IEEE 802.1Qspecification.

As shown in both FIGS. 5 and 7, two different bit rates are used for thetransmission of the bits in the transmission frame. The exact changeoverposition BRSP is specified in both figures. The bit-rate switches fromslow to fast between the BA and DL fields, and from fast to slow betweenthe CRC and EOF fields.

The slower bit rate is designated as bit rate Slow.

The faster bit rate is designated as bit rate Fast.

For the Slow bit rate a range between 500 kbps and 1500 kbps isspecified. All bit rates in operations of 250 kbps are also supported.

For the Fast bit rate a range between 2000 kbps and 12000 kbps isspecified. In this range all bit rates in 1000 kbps operations will besupported.

Higher bit rates for the Slow bit rate and the Fast bit rate canoptionally be supported.

The Bus Arbitration field BA is used for bus arbitration, as in the CANbus. In principle, the definition of the identifiers for the messages isnot subject to any restrictions.

Nevertheless, from the perspective of optimizing the bus for thetransmission of IP packets, it is helpful to apply an assignment policywith regard to the ID assignment.

The compliance with the assignment policy is particularly beneficial inthe field of IP communication.

As in the case of the CAN bus and CAN FD, the identifier is used toimplement a prioritization concept. The identifier is used as a basisfor deciding which CAN node is prevalent on the bus. The bus accessmethod corresponds to the CSMA-CR method (Carrier Sense Multiple Accesswith Collision Resolution). The CSMA/CR method ensures thattransmit-ready CAN nodes only access the CAN bus when it is free. In thecase of simultaneous bus accesses, the method of bitwise bus arbitrationwhich underlies the CSMA/CR method ensures that the CAN node with thehighest-priority CAN message will always prevail. In principle, thefollowing applies: the higher the priority of a CAN-message, the soonerit can be transmitted on the CAN bus.

Under an unfavorable system design, low-priority CAN messages even runthe risk of not being transmitted at all. Therefore, the assignment ofthe IDs is very important for the implementation of a deterministic datatransfer.

According to the new concept, the 32 bits of the identifier are brokendown into two fields [Message Content] and [Device].

The [Message Content] field comprises the higher-value bits of theidentifier.

The [Device] field comprises the lower-order bits of the identifier.

The size of the individual fields can be selected in line withrequirements, but must be the same for all subscribers within a CANnetwork. In an exemplary embodiment, 24 bits are reserved for the[Message Content] field and 8 bits for the [Device] field. It istherefore possible to apply a fine differentiation with regard to thepriority of messages in the network. If two subscribers want to send amessage with the same priority at the same time, then the decision as towhich subscriber device receives the priority is made in the [Device]field.

A lower binary number in the [Message Content] or [Device] fieldcorresponds to an actually higher priority. In the arbitration phase thedominant bus level always prevails on the CAN bus. A CAN node whichdetects that it itself has only sent the recessive bus level, butdetects that the dominant level is present, concedes in the arbitration.

By the appropriate assignment of the Device ID, one bus node can begiven priority over the other subscribers on the bus. As a result, thenetwork behavior becomes predictable and is therefore real-time capable.

FIG. 8 illustrates the process of arbitration.

In the upper part of the figure the individual bit positions of theArbitration Field BA are numbered from 0 through 31. In the [MessageContent] field, for each bit the priority associated with the individualbit position is also specified. The bit position ID8 in the [MessageContent] field is assigned the lowest priority Priority0 andaccordingly, the bit position ID31 is assigned the highest priorityPriority23 in the [Message Content] field. Likewise, the bit with thenumber ID0 in the [Device] field has the lowest priority and the bitwith the number ID7 then has the highest priority.

In the middle section of FIG. 8 an arbitration process is shown wheretwo control units St. A and St. B are competing for access to the bus.The St.A control unit has been assigned the device ID 00000010b and thecontrol unit St.B has been assigned the device ID 00000011b. In thiscase, the bus assignment is decided in the [Message Content] field. Inthe case illustrated, the subscriber St.B wins because it has entered a“0” in bit ID9 and the subscriber St. A has entered a “1” there. Anentry of “0” corresponds to the dominant bus level in the CAN bus.

In the lower section of FIG. 8 an arbitration process is shown, whereagain the two control units St. A and St. B are competing for access tothe bus. In the [Message Content] field both subscribers send the sameCAN message, and so here the same ID is sent in the [Message Content]field. Therefore the bus assignment in this case is not decided untilthe [Device] field. In the case shown, the subscriber St. A wins,because it has entered a “0” in the last bit with the number ID0 and thesubscriber St. B has entered a “1” there.

In a simplified variation, all 32 bits of the identifier are used forthe message content identification and prioritization. The deviceaddressing is performed solely by the MAC addresses which are alsotransmitted in the modified transmission frame.

The disclosure is not limited to the exemplary embodiments describedhere. There is scope for various adaptations and modifications, whichthe person skilled in the art due to his expertise would also consideras belonging to the disclosure.

All examples mentioned herein, as well as conditional formulations, areto be understood as being without limitation to such specificallymentioned examples. Thus, for example, it will be acknowledged bypersons skilled in the art that the block diagram shown here representsa conceptual view of an exemplary circuit arrangement.

It should be understood that the proposed method and the associateddevices can be implemented in various forms of hardware, software,firmware, special processors or a combination of these.

Special processors can comprise application specific integrated circuits(ASICs), Reduced Instruction Set Computers (RISC) and/or FieldProgrammable Gate Arrays (FPGAs). Optionally, the proposed method andthe device are implemented as a combination of hardware and software.The software may be installed as an application program on a softwarestorage device. Typically, this will be a machine based on a computerplatform, which has hardware such as one or more central processingunits (CPU), a random access memory (RAM) and one or more of theinput/output (I/O) interface(s). In addition, an operating system istypically installed on the computer platform. The various processes andfunctions which have been described here can either be part of theapplication program, or executed as part of the operating system.

LIST OF REFERENCE SYMBOLS

-   10 transportation vehicle-   21 matching circuit-   22 simplified CAN transceiver-   23 extended Ethernet PHY-   24 switch-   25 microprocessor-   100 transportation vehicle electronics-   102 data bus—driver assistance-   104 data bus—drive-   106 data bus—suspension-   111 driver assistance control unit-   112 RADAR control unit-   113 ultrasonic sensor control unit-   121 engine control unit-   122 ESP control unit-   123 transmission control unit-   124 wheel speed sensor-   125 wheel speed sensor-   126 wheel speed sensor-   127 wheel speed sensor-   131 suspension control unit-   132 power-assisted steering control unit-   140 gateway-   BRSP bitrate switchover point

The invention claimed is:
 1. A method for transmitting data over atransportation vehicle CAN serial communications bus, wherein the datais transmitted with a CAN bus modified transmission frame, wherein themodified transmission frame has at least one arbitration field and onedata field, wherein the arbitration field is used to controltransportation vehicle CAN bus access according to a Carrier SenseMultiple Access with Collision Resolution method, by prioritization ofmessages based on an identifier, and wherein a low bit rate is set fortransportation vehicle CAN bus arbitration data in an arbitration phaseand a higher bit rate is set in the data field for the transmission ofthe transportation vehicle CAN bus data, the method comprising:providing a start field in the modified transmission frame; andpackaging the data as an Ethernet transmission frame which is insertedinto the data field of the CAN bus modified transmission frame, whereinthe arbitration field and the start field replace a preamble and a startframe delimiter of the Ethernet transmission frame.
 2. The method ofclaim 1, wherein the identifier in the arbitration field is sub-dividedinto a “Message Content” identifier section and a “Device” identifiersection.
 3. The method of claim 2, wherein a higher-order bit section isreserved for the prioritization of the message content and a lower-orderbit section is allocated to the device identification.
 4. The method ofclaim 3, wherein the identifier has a length of 32 bits and thehigher-order bit section has a length of 24 bits and the lower-order bitsection has a length of 8 bits.
 5. The method of claim 1, wherein thedata field has a variable length up to a fixed upper limit.
 6. Themethod of claim 5, wherein the fixed upper limit relates to the value of4096 bytes.
 7. The method of claim 1, wherein the length of thearbitration field is set to 32 bits.
 8. The method of claim 1, wherein aCRC check code provided in the Ethernet transmission frame is replacedby an extended CRC check code which is inserted into an extended CRCfield of the modified transmission frame, wherein the extended CRC checkcode is calculated over the start field, arbitration field, a controlfield, a destination address field, a source address field, an optionalQ-TAG field, a type field, a data field and the section of the stuff-bitcounter in the CRC field.
 9. The method of claim 8, wherein the datatransmission takes place asynchronously and a resynchronization isperformed according to a bit-stuffing rule to ensure synchronization ofa data transmitting station and a data receiving station, wherein thebit-stuffing rule is applied over the ranges from the start field to theend of the data field, wherein the bit-stuffing rule states that astuff-bit is only inserted after a defined number of successive bitswith the same transportation vehicle bus level, wherein the definednumber is a natural number greater than the number 5 and wherein thenumber of inserted stuff-bits is entered in one section of the extendedCRC field.
 10. The method of claim 8, wherein a stuff-bit is inserted atfixed specified positions in the CRC field.
 11. The method of claim 10,wherein the extended CRC field starts with a fixed specified stuff-bitand the other fixed specified stuff-bits are each inserted at aninterval of 9 bits of the CRC field.
 12. The method of claim 1, whereinan end field is provided in the modified transmission frame and at leastone end-of-frame code is entered in the end field, wherein theend-of-frame code has a length of 11 bits.
 13. The method of claim 1,wherein the Ethernet transmission frame is an Ethernet transmissionframe based on IEEE 802.1Q.
 14. A bus interface for use for transmittingdata over a transportation vehicle CAN serial communications bus,wherein the data is transmitted with a modified transmission frame,wherein the CAN bus modified transmission frame has at least onearbitration field and one data field, wherein the arbitration field isused to control transportation vehicle CAN bus access according to aCarrier Sense Multiple Access with Collision Resolution method, byprioritization of messages based on an identifier, and wherein a low bitrate is set for transportation vehicle CAN bus arbitration data in anarbitration phase and a higher bit rate is set in the data field for thetransmission of transportation vehicle CAN bus data, wherein a startfield is provided in the modified transmission frame, and the data ispackaged as an Ethernet transmission frame which is inserted into thedata field of the CAN bus modified transmission frame, and wherein thearbitration field and the start field replace a preamble and a startframe delimiter of the Ethernet transmission frame.
 15. The businterface of claim 14, wherein the identifier in the arbitration fieldis sub-divided into a “Message Content” identifier section and a“Device” identifier section.
 16. The bus interface of claim 15, whereina higher-order bit section is reserved for the prioritization of themessage content and a lower-order bit section is allocated to the deviceidentification.
 17. The bus interface of claim 16, wherein theidentifier has a length of 32 bits and the higher-order bit section hasa length of 24 bits and the lower-order bit section has a length of 8bits.
 18. The bus interface of claim 14, wherein the data field has avariable length up to a fixed upper limit.
 19. The bus interface ofclaim 18, wherein the fixed upper limit relates to the value of 4096bytes.
 20. The bus interface of claim 14, wherein the length of thearbitration field is set to 32 bits.
 21. The bus interface of claim 14,wherein a CRC check code provided in the Ethernet transmission frame isreplaced by an extended CRC check code which is inserted into anextended CRC field of the modified transmission frame, wherein theextended CRC check code is calculated over the start field, arbitrationfield, a control field, destination address field, a source addressfield, an optional Q-TAG field, a type field, a data field and thesection of the stuff-bit counter in the CRC field.
 22. The bus interfaceof claim 21, wherein the data transmission takes place asynchronouslyand a resynchronization is performed according to a bit-stuffing rule toensure synchronization of a data transmitting station and a datareceiving station, wherein the bit-stuffing rule is applied over theranges from the start field to the end of the data field, wherein thebit-stuffing rule states that a stuff-bit is only inserted after adefined number of successive bits with the same bus level, wherein thedefined number is a natural number greater than the number 5 and whereinthe number of inserted stuff-bits is entered in one section of theextended CRC field.
 23. The bus interface of claim 21, wherein astuff-bit is inserted at fixed specified positions in the CRC field. 24.The bus interface of claim 23, wherein the extended CRC field startswith a fixed specified stuff-bit and the other fixed specifiedstuff-bits are each inserted at an interval of 9 bits of the CRC field.25. The bus interface of claim 14, wherein an end field is provided inthe modified transmission frame and at least one end-of-frame code isentered in the end field, wherein the end-of-frame code has a length of11 bits.
 26. The bus interface of claim 14, wherein the Ethernettransmission frame is an Ethernet transmission frame based on IEEE802.1Q.
 27. An article, comprising a computer program, wherein thecomputer program includes instructions for execution by a processor fortransmitter-side operations and/or receiver-side operations of a methodfor transmitting data over a transportation vehicle serialcommunications bus, wherein the data is transmitted with a modifiedtransmission frame, wherein the modified transmission frame has at leastone arbitration field and one data field, wherein the arbitration fieldis used to control transportation vehicle CAN bus access according to aCarrier Sense Multiple Access with Collision Resolution method, byprioritization of messages based on an identifier, wherein a low bitrate is set for transportation vehicle CAN bus arbitration data in anarbitration phase and a higher bit rate is set in the data field for thetransmission of transportation vehicle CAN bus data, wherein a startfield is provided in the modified transmission frame, and the data ispackaged as an Ethernet transmission frame which is inserted into thedata field of the modified transmission frame, and wherein thearbitration field and the start field replace a preamble and a startframe delimiter of the Ethernet transmission frame.